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Nov. 25,' 1952 w. M. BARKER ALTERNATE ROUTE SYSTEM FOR CENTRALIZEDTRAFFIC CONTROL.

Filed NOV. 50, 1950 2 SHEETS-SHEET 2 JIM w Patented Nov. 25, 1952 AyrnRATE ROUTE SYSTEM FOR CEN- TRALIZED TRAFFIC CONTROL W ll am MafiarkerSwttsville, a isnor o. General Railway Signal Company, Rochester,

Application November 30, 1950, Serial-No. 198,386

C a m This invention relates.- to' a. centralized traffic controlsystem, and; more particularly pertains to a centralized trafiiccontrolsystem in which controls and indications may be transmittedbetween control office andfield stations either over the usual linewires or overan alternate route.

In a centralized traffic control system (commonly abbreviated CTC) theswitches, signals, and otherassociated apparatus along a trackway areremotely controlled from a control office by the transmission of controlcodes from the control office to the various field stations at whichsuch apparatus is located. Indications astothe actual operatedconditions of the various devices and such other information as may bedesired are, in turn-, transmitted from each field station to thecontrol oifice. These controls and indications are transmitted overapairof line wires connecting the control ofiice to each of the fieldstations. In the eventr of failure of these line wires such as an opencircuit, transmission between the control ofiice and the field stationslocated beyond the fault becomes impossible. When the line faultoccursneanthe control office, transmission to most of the field stations isprevented so that the system becomes' almost entirely inoperative. Toovercome this difliculty, the present system provides that controlsforstations to the far side of the fanlt maybetransmitted over an alternateroute directly to the last field station, i. e. the field statien mostre mote from the control office along the normal line wire channel.('3omrnunication-- may'then be had with those field stations bytransmitting from the site of the last field station over the normalline wires to the location of the fault. The field stations on the nearside of; the fault may be communicated with by transmitting i rectlyfrom the control oflice over the normalline wires to the fault.Indications may be transmitted over these same channels. In this way,communicationsmay be maintained between the control oiiice and all ofthe field stations despite the fault in the line wires.

At the site o f the last fieldstation, a 'c onk to the indication codesoriginating at the various fiel s t o ss ated. herew th. b ausin O TSPQnding, code, o. b ansmi ttq' bac *0 the. n l Q fi A t. of is,nvention is, to, provide a converter unit. which causes the line.current to increase rapidly to the proper value uponthe enc o v node.pulse. so. n tov provide for, quicker energiaation of the line relay ateach field station.

Another object of this invention to provide a converter unit that itcapable of transmitting indications to the control office evenwhenfailure occurs. in the control code channel,

Another object is to provide apparatus at the controlofiice permittingthe selective use of either I the normal line wires or thealternateroute,

Still another object of this invention is to pro vide a converter unitwherein, the. alternate. en-, ergization and deenergization of the CTCline wires will notresultin operation of the line relay included in the.converter unit.

Other objects, purposes, and characteristic features of this; inventionwill be in partobvious trom the accompanying drawingsv and in part madeclear from the description of. the invention.

In describing the invention in detail, reference will be made to theaccompanying drawingsin wh chlike, efer n e a a si natrrespondingpartsin the several views and in which;

F l st te in oc o he al ern t route system of the present inventionadapted to a typical CTG system; and

Figs- 4. a d .15am ir u t d w ng S ow n in detail he rgan at on of heQni r uni and also a portion of the control achine. apparatus The partsand circuits of this invention are shown diagrammaticallyandconventional illustrati ns are use to sim ifryh dra g and theexplanations. Ijhe drawings havebeen made to make it easy to understandthe. principles and manner of operation of this invention rather thanto, show the specific construction and arrangement of parts that wouldbe used in practice. Relays and their contacts are shown in theconventional way. Symbols are used to indicate connections to theterminals of a battery or other source of electric powerinstead ofshow,ing all of the wiring connections to these terminals.

The way in which this alternate route control is applied to a typicalCTC- system is shown in general form in Fig. 1. The GTO system may-be ofany well known kind and may, for example, be of the kind shown in Pat.No. 2,393,756 1 t9 Hailes, et al., dated April 27, 1943. For thepurobtained by referring to the cited Hailes, et al. 1

patent.

General organization Referring to Fig. 1, a control machine 9 isprovided to enable an operator at a remote location to control theoperation of various apparatus at a number of field stations locatedalong a trackway. Normally these controls are transmitted from thecontrol location by the transmission of electrical pulses over a pair ofline wires I9 and II. The various field stations such as those indicatedin the blocks l2, l3 and M are controlled by these electrical pulsesappearing on the line wires l and II and in turn transmit indicationsover these same line wires to the control machine 9. If a line faultsuch as an open circuit occurs in the line wires 10 and II,communication between the control machine 9 and the field stationslocated on the near side of the fault can still be maintained in thenormal manner. To permit communication with the remainder of the fieldstations, the operator at the control machine 9 can, by operating asuitable transfer switch included in the control machine, cause thecontrol codes for such field stations to be transmitted instead to atelephone exchange or some other suitable facility such as a telegraphcompany. The telephone exchange then transmits the control as receivedfrom the control machine 9 over available facilities to a similarexchange l6 located in the vicinity of the last field station in thesystem. Indications are similarly transmitted over another channel fromthe telephone exchange 16 to the similar exchange 15. Thesetransmissions between the two telephone or telegraph offices can be byany suitable means such as direct-current pulses, line wire carrier, ormicro-wave radio. For purposes of illustration,

communication between telephone exchanges is an arrangement is believedto be less desirable,

however, in that such a route would parallel the original CTC line andmight very well be affected by the same trouble that has rendered thenormal line unusable over its complete length. Furthermore, an alternateroute is presumably to be used only infrequently so that it iseconomically sounder to contract for the use of the needed facilitiesonly as they are occasionally required. The telephone exchange I6 isconnected to the converter unit ll by two pairs of wires; one for thetransmission of controls, and the other for indications. The converterunit is normally not connected to the line wires I9 and H, but can be soconnected by closure of the switch contact I? when it is desired to usethe alternate route.

The CTC system of which this alternate route system is a part, ispreferably a shunt-type system. In a shunt-type system, the line wiresconnecting the control ofiice with the various field stations arenormally energized, and the code characters constituting the controlcode are provided by alternately energizing and deenergizing the linewires. The transmission of indications from any field station to thecontrol ofiice is accomplished by alternately shunting and unshuntingthe line wires at the transmitting field station.

When the alternate route is used, the control code originating at thecontrol machine 9 is transmitted over such route to the converter unitI! which then responds by alternately deenergizing and energizing theline wires l0 and l l in correspondence with the nature of the controlcode. Similarly, for the transmission of indications this converter unitI! is responsive to the alternate shunting and unshunting of the linewires by the field stations which are located between it and the faultin the line wires to control the operation of the apparatus in thetelephone exchange I6 for transmission of an indication code over thealternate route line wires, and through the telephone exchange |5 to thecontrol machine 9.

Detailed circuit The detailed circuits shown in Figs. 2A and 2Bcorrespond to the block diagram of Fig. 1, with the exception thatvarious blocks have been shown in greater detail. Only the portion ofthe control machine 9 directly associated with the operation of analternate route link is shown in Fig. 2A. Various relays are shown, butexcept for the transfer relay TN, these relays are all energized in thesame manner as the correspondingly designated relays in the previouslymentioned Hailes, et al. patent. The relay F has three windings, and thecircuit for the energization of one of these windings is as illustratedin Fig. 2A. The remaining windings of this relay are energized in thesame manner as illustrated in the Hailes, et al. patent.

The transfer relay TN controls whether the normal CTC line wires or thealternate route is to be used. This relay is controlled by a contact 20which causes relay TN to be deenergized when it is desired to transmitover the usual line wires, and causes the energization of this relaywhen transmission is to be made over the alternate route. Thus, when abreak occurs in the usual line wires, the contact 29 must be moved tothe normal line position to effect communication with the field stationson the near side of the line break, but must be moved to the alternateroute position when communication is to be had with field stations tothe other side of the line break.

When the system is at rest and the normal CTC line is to be used, thevarious relays at the control ofilce are in the condition shown in Fig.2A so that only the relay OR is energized. As a result, line wire In isconnected through back contact 22 of relay TN, back contact 23 of relayCF, back contact 24 of relay C, and front contact 25 of relay OR, to theside of battery 2|. At the same time, line wire II is connected throughback contact 21 of relay TN, back contact 28 of relay CF, back contact29 of relay TN, back contact 30 of relay TN, and through the primarywinding of pulse transformer 25, to the opposite terminal of battery 2|.Consequently, steady energy is applied to the line Wires i0 and l I.During a control cycle, relay OR becomes deenergized and relay C becomesenergized. Also, relay E is then selectively energized and deenergizedin accordance with the nature of the control code to be transmitted.During a con- "these line wires.

chrome .5 tr-cl :cycle, line wire 10 is connected through back contact22 .of relay back contact 23 of relay cn-mm contact 121! .of :relay :C,.and front contact 35 :of relay B when this relay is picked up, to the1+) side of battery 2!. Line'wire H remains connected .to the 1- side ofbattery '2l through the same circuit already described. Thus, when relayE :is dropped away, the line wires and H are notconnected tothe oppositeterminals :of battery .21 so that these line wires :are deenergized.Each time thatrelayiEiis picked up, :however, direct-current energy :isapplied "to the line wires 10 and .11.

If a break occurs in the line wires TH] .and H "and the operator at thecontrol machin :9 wishes to transmit controls or receive indicationsfrom "the field stations .to the far side-of the line break,

he operates the lever'2'0 ftoithe alternat route position to energizerelay TN. The resultant opening-of back contacts ;22 and '21 of this:relay "opens the circuit to the .line wires J ll and H .so

that electrical pulses cannotbe transmitted over Instead, a circuit isthen completed when the system .is at rest from the side-of battery 2:!and through frontcontact 25 of relay'OR, back contact '24 of relay C,back "contact 23 of relay CF, vfront contact '22 of relay "TN, frontcontact 2101 relay TN, :back contact 28 of relay "CF, frontcontact '29of relay TN over wire t9, through resistor 36 and the windings of therelay CT includedin the telephone exchange 1 5, over wire 33 and throughfront contact 30 of relay TN and'the primary winding of transformer 26,to the opposite terminal of battery ill. Therefore, during a period of:rest but with relay TN energized, the control transmitting relay CT issteadily energized. With :front contact 31 of relay CT closed, :acircuit is completed 'throughbattery 31 to energize relay :ICR at thetelephone exchange l5 over the alternate route lline wires 32.

During a control cycle in alternate route transmission, a similarcircuit is established for the-en- -.ergization of relay CT with theexception that this'oircuit includes from contact 35 of relay E andfront contact 24 of relay C instead of front contact 25 of relay OR andback contact 24 of relay C. In this way, the energization of relay CT.is dependent upon the action of the *com-. "mutatingrelay E. When'fron't contact35 of relay E "is closed relay CT is ener'gized, and withthis front contact 35 open, relay CT is deenergized. "Thus, as frontcontact 31 of this .relay CT is alternately closed and opened, thecontrol run-r riin'g 'relay I'CR at the telephone exchange it iscorrespondingly energized and deenergized.

During a control cycle, relay C is energized so that its back contact40"is open, thereby prevente ing energization of the upper winding ofrelay- F in response to the voltages induced in the secondary winding ofpulse transformer 25 :by changes-of current in the primary winding. Onlyduring *an indication cycle as will later be described, when relay 0 isreleased, can the'F relay have-its upper winding energized in responseto "thecurrent changes in the primary winding of transformer 26. g Tosummarize, the operation of this part of the control machine 9 is suchduringa control cycle as to selectively energize the line wires l0 andgized, the Iline wires l0 and H are no longer energized, and instead acircuit is provided .to 1

line wires selectively energize and deenergize relay CT included in thetelephone exchange l5, subject again to the action of front contact '35of the commutating relay E. A contact 31 of this relay CT is theneffective over the circuit includin the alternate route wires 32 andbattery 31 to means between the telephone exchanges'will be.

provided only when required. Under those circumstances, back contact -41of relay 1GB is normally closed so that relay 20R would normally beenergized. power consumption, battery '46 is normally disconnected as by:a manually operable switch "48. Then on the infrequent occasion whenthealternate route is to be used, this switch contact is closed.

'As already explained, when the alternate route is used but during arest period, relay CT is energized. Consequently, relay iCR is alsoenergized with its back contact 41 open so that relay 2GB isdeenergized. During a control cycle, each deenergization of relay CTcauses the deenergization of relay 40R and the picking up of relay 'ZCR.

When the system is at rest, the various relays at the converter unitassume the positions shown in Fig. 2B. In alternate route operation, thecontacts of switch [8 are assumed to be closed. Manual operation of thisswitch It may be .obtained by telephone communication between thecontrol machine operator and a maintainer who will be instructed toclose the switch contacts 18 for alternate route operation. Contact 4'3at the telephone exchange'lB is, at the same time, operated to itsclosed position. The output wires of the converter unit ll are thusconnected to the line wires Ill and H at the iar end of the ETC line.Line wire l Otis then connected through a back contact 'of relay PC andthrough current-limiting resistor 5 to the (-1-) side of a battery 52.At the same time, line 'wire'll is connected through back contact 53 ofrelay ZPC, back contact 5'4 of relay 20R, and the primary winding ofa-pulse transformer 56 to the opposite terminal of battery 5-2.Therefore, the line wires Hi and l I are energized with direct-currentenergy during a period of rest. Thus, 'the'condition establishedcorresponds with that provided for field stations located on the otherside of the line 'fault which are similarly energized during a period ofrest when the transfer relay TN is in a released condition.

Each time that the normally deenergize'drelay 2GB. at the converter unitlocation becomes energized, its front contact '54 closes sowthat the Itand H are connected together through the discharge resistor '55. At thesame time, this closing of front contact 54 shuntsthe battery '52through the current-limiting resistor 51 and the primary winding ofpulse transformer 55. The resulting resistance in this shunt path forbattery '52 is less than that presented by the line wires l9 and H sothat the current supplied by battery. '52 and'passing To preventunnecessary battery 52 actually decreases.

through the primary winding of pulse transformer 56 is actuallyincreased at such time even though no energy is then supplied to theline wires IE3 and H. Each time that back contact 54 of relay 2GB isclosed, thereby connecting line wires H) and H to the opposite terminalsof battery 52, the current supplied by In most of the systems of theprior art, the current through the line wire circuit including the pulsetransformer decreases to zero during the off periods of the code. At thebeginning of an on period when the line wire circuit is again energized,the rise of current is impeded by the transformer inductance so that thebuild-up of current in the line wires proceeds but slowly. With thecircuit organization of the present invention, however,

.the current is not decreased during the code offperiods but is actuallyslightly increased. For two reasons, this allows the current in the linewires to reach its normal value for a period -of energization morequickly. The first is that the difference in current through thetransformer winding between the on and of? periods of the code isreduced so that the transformer inductance has a smaller effect upon thechange of current taking place. The second reason is that the directionof change in the current at the beginning of a period of energization,i. e. a decrease, induces a voltage in the primary winding oftransformer 56 which is of such a polarity that it tends to maintain thecurrent through the winding at its previous higher value. Consequently,the polarity of this voltage is such as to add to the battery voltage,thereby momentarily increasing the voltage applied to line wires l and Habove the normal voltage supplied by battery 52. This momentaryhigher-than-normal voltage aids in building up the current in the linewires to the full, steady-state value with the result that the linerelays at the associated field stations are more quickly picked up.

As the current through the primary winding of the transformer 55alternately increases and decreases during a control cycle subject tothe operation of contact 5d of relay ECR, a corresponding voltage isinduced in the secondary winding of this transformer. It is desirable,however, that relay FR, connected across the secondary winding throughback contact 5? of relay 20R, not be energized to its oppositeconditions in response to these induced voltages. R lay FR is a polarrelay, and its contacts remain in the position to which they are lastactuated. When current passes through the windings of this relay fromleft to right, the contacts of this relay are operated to theirright-hand position; and when current passes through the windings ofthis relay from right to left in the drawing, this relay is energized sothat its contacts move to their left-hand positions. As will presentlybe described, relay FR is normally in the condition wherein its contactsare in the right-hand position.

Each time that front contact 54 of relay ECR is closed, the currentthrough the primary winding of transformer 56 is increased as previouslydealso assume a positive'potenti-al with respect, to

the left-hand end. Consequently, the current passing through thewindings of relay FR would ordinarily be in the direction from right toleft and would cause this relay to be energized so as to operate itscontacts to their left-hand positions. To prevent this undesiredoperation, each energization of relay ZCR opens back contact 5! andinstead provides a circuit through front contact 5! to As a result,current is supplied from this terminal and through the windings of relayFR to and the direction of this current is such that the contactsof thisrelay remain in their right-hand positions.

Each time that relay ZC-R becomes deenergized, the closure of backcontact 54 connects the battery 52 to the wires l0 and II with aresulting decrease of current supplied by battery 52. This decrease ofcurrent induces a voltage in the primary winding of transformer 56 sothat righthand' end of this primary winding becomes positive withrespect to the other end. The secondary winding thus has a voltageinduced in it with the polarity causing the left-hand end to becomepositive with respect to the other end of this prim-ary winding. Thispolarity of voltage causes current to pass through the back contact 5'!of relay 20R and the windings of relay FR in the direction from left toright. With this polarity of energization, the contacts of relay FRagain remain in their right-hand positions. Thus, the energization ofrelay FR. is unaffected by the intermittent operation of relay ZCRduring a control cycle. This result is accomplished by eitherdisconnecting relay from the secondary winding of transformer 55 whenthe induced voltage across this secondary winding would be such as tooperate the contacts to their left-hand positions or by causing theinduced voltage to be of such a polarity that the direction of currentpassing through the windings of relay FR will not cause the contacts tobe operated to the left-hand positions.

When any field station desires to transmit an indication to the controloflice, the conditioning period of such an indication code is initiatedby the shunting of the line wires 10 and H at that field station. Thisshunting of the line wires increases the current supplied by battery 52and, as previously explained, an increase of current through the primarywinding of transformer 56 causes a current fiow through the circuitincluding back con-tact 51 of relay ZCR and the windings of relay FR ofsuch a direction that the contacts of this relay are operated to theirleft-hand positions. When this actuation of relay FR occurs in theconditioning period of an indication cycle, a circuit is completedthrough the back contact 58 of relay 20R, left-hand contact 59 of relayFR, back contact 60 of relay PC, and the windings of relay FP, toConsequently, relay FP becomes energized and its front contact BI isclosed. The closure of this front contact 61 connects the left-handterminal of the secondary winding of transformer 56 to thereby shuntingthe secondary winding of this transformer with the result that changesof current in the primary winding can no longer aifect the energizationof relay FR. As soon as relay FP becomes energized, its front contact 62also becomes closed so that a circuit is completed through the contacts58 and 59 and through this front contact 62 and the windings of relayPC, to This circuit permits the energization of the pole-changing relayPC. One result of the energization of this relay PC is that the closureof its front contacts 50. and 53 re- 9 verses the polarity of theenergization applied to' wire's l0 and II. This reversal of polarity'isrequired tolock out all other field stations to preventtheirtransmitting indications when one of the stations has already begun totransmit its indication. Also, when relay PC picks up, its back contact60 opens so th-at the energizing circuit for relay FF is interrupted.Therefore, relay FP drops awayaand the opening of its front contact 62opens the pick up circuit just described for the energization of the"pole-changing relay PC. Since thepicking upof relay PC has caused astick circuit to be'completed throughback contact 58 of relay ZCR, backcontact ll of relayFP, and front contact of relay PC, this relayremainsenergized even through its pick up :circuit is opened'by thedroppingtawayof thecontacts of'relay FP. Relay PC is providecl'with slowrelease characteristics so that it will rem-ainpicked up'during thecrossovertime of itheconta'cts of relay FP. In other words, -the releasetime of relay PC must be'sufiicient sothat it will remain picked up fromthe "time v.itspick up vcircuitis broken by the opening offronttcontacttZ until the closing of back contact H compl'etes'its stickcircuit. When relay PP drops away, its front contacts] also opens sothatthe shunt on the secondary winding of pulseitransformer ifi is removedand relay FR' 'canLagain' become responsive to the changesof current inthe. prim'arywinding :ofthis'ftransformer.

' To summarize, the first energization of "relay FR withits contacts"moving to their left-hand positions causes the energization of frelay.FP.

Thepicking up of relay FP thenlcompletes-a pick up circuit for relay'PC,"and 'whenthis latter relay picks up a stick circuit is completed tohold it inthat condition. Thepicking up of relay PC also causes thel'deenergization of relay FP. Thus, relay FP is, in 'elfect, picked uponly .4

for the time required for relay- PC- to become energized :and close itsfront contacts. The purpose of this operation is to permit shunting ofthe secondary winding of transformer 56 during the time that 'relay PCis picked upand the polarity of energization to the wires I0 and Hreversed. -In this way, relayFR cannot be affected by the change ofcurrent resulting from the pole-changing operation.

During the conditioning period 'of' anindica- 3 store'sthe normalpolarityof energy'to the line wires and thus; permits any ofithe lfieldstations to transmit "an indication. To "ensure that the control ofliceapparatus is properly conditioned to receive such further indications,it is desirable ---that the control for the :relea'se rof i relay -PCoriginate at the control ofiice an'd-f be tr anstn'itted when thecontrol oflice apparatus is thus properly conditioned. If, 'however, x afault should "occur in "the alternate route link -t'o prevent the'pick-'ing up :oftrelay 'ZCR, :back contact 58 remains closed so that relay PCcannot become deen'er- .gized. 'Asya result, the line "wires F I'O a'n'dI l re- 10 main-pole-changed so"thatindications-wannotzbe transmittedfrom the various 'field' stations ll'ocated-be'tween the :end ofthe linewires and :the fault in tlie line wire link. 'CheckrelayaCC is includedin the "apparatus comprising the converter unit l-l to prevent thisundesired. lock out of intlications in the event of failure oftheoutbound channel provided for the transmission .of controls.

During the time that "the system is fat .irest, relay CC is e'ne'rgize'dthrough a-ci'rcuit from and including back contactts of relay CR, backcontact H of relayiFP, back contact 10 of relay PC, 'and through thewindings of relay CC to Thus, relay CC is steadily energizedduring aperiod of rest. During a control cycle, back contacts 10 and H of relayPC and FPrespectively remain closed. Each time that back contact 58 isclosed, relay CC is momentarily energized. This relay CC is providedwith slow'release characteristics as indicated by the base line for thesymbol designating this relay so that it remains picked up during acontrol cycle despite the intermittent'nature of its energization.

During an indication cycle, relay PCis maintained in a picked upcondition so that the abovedescribed circuit for the energization ofthecheck relay CC is opened by the opening of back :contact 10 of relayPC. Throughout an indication cycle, however, contact 59 of relayFR isalternately operated between its left and right-hand position. Eachtimethat contact 59 of rela'yFR is operated to its left-hand position, acircuit is completed from through back contact 58 of relay 2CR,1eft-hand contact 59 of relay FR, front contact 13 of relay PC, andthrough the windings of relay CC'to Although relay CC is thusagainenergized only intermittently, it remains picked up because of itsslow releasing characteristics.

"In the event that relay 2CR cannot be picked up, the first indicationcycle originating at a field station located between the converter unit11 and the fault in the line wires will be correctly transmitted overthe alternate'route back to the control machine 9 because the lock outof indication transmissions does not occur until the transmission of anindication cycle has caused thepole-chang-ing relay PC to be picked upand held in that condition by the failure of the out- :bcund channel forcontrols. At the end of-such first indicationcycle, however, contact 59of relay FR' rem'ainsin its right-hand position resulting inthe openingof the circuit for the energization 'o-f relay CC. As a result, relay CCdrops away after a short interval corresponding to the slow releasingcharacteristics of this relay. 'Theresultan-t closure of back contact"of relay-"CC closes a circuit for the energization of relay FP whichcircuit includes this-back contact 14 and front contact'liil of relayPC. RelayFP picks 'up and in-doing so opens its back-contact'll which isincluded in the stick circuit for relay PC. Relay PC, therefore, dropsaway thereby closing its back contacts-50 and-53 so as torestoreth'enormal polarity of energization to the line Wires IF-and :l5. At the same time, front contact fifl of'relay PCisopnedso-that relayFF is againquickly deenergized. The'result of the "above-describedoperation"involving'relay CC is 'thatthedmpping away of' thisrelayca-uses first the picking up of relay FP followed,"inturn,"by thedeenergization of relay 'PC. When relayPC is finally'released,relay-FP"also becomes released. Thus, once-again relay FP is operatedto'close'its" front contacts during the time that the line wires and I lare pole-changed by the relay PC so that, with front contact 6| of relayFP closed during this interval, the secondary winding of transformer 56is shunted with the result that the line relay FR is not affected by thepole-changing operation. With the line wires [0 and H again steadilyenergized with the normal polarity, the various field stations locatedbetween the end of the CTC line and the fault in the line can againtransmit their indication codes over the alternate route link to thecontrol machine 9.

Although the means thus provided ensures that relay PC will not remainpicked up at the end of an indication cycle, it is still considereddesirable that this control of relay PC be normally initiated atthecontrol ofiice. The slow release characteristics provided for relayCC must be such that the drop away of relay PC caused by the droppingaway of relay CC does not occur until the control office apparatus hasbeen restored to its normal condition. A fixed time interval must thusbe added and to allow continually for this longer period of time slowsup the rate at which successive indication can be transmitted. Also,since relay PC cannot be dropped away until the control oilice apparatusis restored, a control transmitted immediately following suchrestoration may occur before the pole-changing operation has taken placeso that such control is not properly received. For this reason, it isadvantageous to cause a positive control to be transmitted from thecontrol office when the control oifice apparatus is cleared out so thatanother indication can quickly be transmitted. The circuit organizationof the present invention does, however, revent a lookout of the variousfield stations in the event that the pole-chan ing relay cannot bereleased.

During an indication cycle, relay IT at the telephone exchange [6 isselectively controlled by contact 12 of relay FR, so that this relay isenergized whenever contact 12 is in its right-hand position butdeenergized whenever this same contact is in the left-hand position. Theapparatus at the telephone exchange i6 is then efiective in response. tothe operation of a contact 16 of this relay IT to control the operationof relay IR at the telephone exchange to by alternately opening andclosing a series circuit including a battery 49 and the winding of relayIR. Front contact of this relay is connected in parallel with a resistorwhich is included in series with relay CT. As previously explained,relay CT is normally energized during a period of rest by having itswinding comiected through resistor to the opposite terminals of battery2!. During this time, the current through the windings of relay CT andalso'through the primary windings of pulse transformer 26 is determinedby the resistance of this circuit. The current in this circuit is alsosubject, however, to the actuation of contact 15. Thus, when frontcontact 75 is closed, resistor 36 is shorted but so that the currentdelivered-by battery 2i to the relay CT is increased. This increase ofcurrent through the primary winding of pulse transformer 26 induces avoltage in the secondary winding thereof. An induced voltage of oppositepolarity appears across the terminals of this winding each time that thecurrent through the primary winding is decreased by opening frontcontact 15.

During a period of rest, back contacts 43, 40 and 39 of relays LV, C andSC respectively are closed so that relay F may be energized by thevoltage induced in the windings oi transformer 26 in the conditioningperiod of an indication cycle. Then when relays SC and CF pick up in theindication cycle as explained in the Hailes et al. Patent No. 2,399,734,the upper winding of relay F is energized first with one polarity andthen the other through a circuit including back contact ii) of relay C,front contact 34 of relay CF, and back contact 43 of relay LV. Contacts63, id, and d5 of relays LV, SB, and SA respectively are included forreasons fully set forth in the Hailes et al. patent. The resultantoperation of relay F in response to the received inclication codes thenmakes possible the required stepping of the stepping banks at thecontrol office during reception of an indication code.

The alternate route link system of the present invention ofiers a meansof greatly reducing delay in train movements in the event of a fault inthe regular line wires used for CTC communication. The organization ofthe present invention is particularly suitable because it permits indication codes to be transmitted even though a failure should occur inthe outbound channel used for the transmission of controls. In addition,the converter organization is so devised that the application of energyto the line wires connecting the converter with the various fieldstations has the effect of momentarily raising the voltage level appliedto the line Wires above that normally applied by the battery used sothat the line relays at the field station may more quickly assume theirpicked up positions. The organization also provides that the line relayat the converter location is unaffected by changes of energization ofthe line wires taking place during a control cycle.

Having'described an alternate route link system as one embodiment of thepresent invention, it is desired to be understood that this form isselected to facilitate in the disclosure of this invention rather thanto limit the number of forms which it may assume; and, it is to befurther understood that the various modifications, adaptations, oralterations may be applied to the specific form shown to meet therequirements of practice, without in any manner departing from thespirit or scope of the present invention.

What I claim is:

1. An alternate route link for a centralized traffic control systemcomprising, a control oflice and a plurality of field stations, a pairof line wires connecting said field stations with said control office,transmitting and receiving means at said field stations and said controloffice for causing controls and indications comprising codeddirect-current pulses to be transmitted between said control ofiice andsaid fieldstations over said line wires, a converter unit located nearthe field station most remote from said control ofhce'along saidlinewires, communications means for transmitting intelligence between saidcontrol office and said converter unit, said converter unit includingtransmitting means governed by the intelligence received from' saidcontrol ofiice for causing a control 'code of'direct-current pulses tobe transmitted over said line wires to said field stations, receivingmeans included in said converter unit responsive to indication codestransmitted from said field stations for causing said indications to betransmitted over said communications means to said control office,whereby communications betweenfsaid control chiefs and said fieldstations is maintained over said line wires and'over an alternate routecomprising said coml mary winding energized by the current in said linewires, a polar relay having its windings connected across the secondarywinding of said pulse transformer in such a manner that actuation ofsaid relay circuit means from its normal condition would operate saidpolar relay from its normal condition, means governed by the actuationof said relay circuit means from its normal condition for disconnectingthe winding of said polar relay from said secondary winding and forenerglzing said relay winding with the polarity to maintain said relayin its normal position, whereby actuation of said receiving means by thetransmission of controls from said control ofiice is prevented.

9. In a system for transmitting controls between a control ofiice and aplurality of field stations, a pair of line wires connecting saidcontrol oifice to said field stations, receiving apparatus at saidcontrol office including a transformer having its primary windingconnected across said line wires and a polar relay having its windingenergized by the secondary winding of said transformer, transmittingapparatus at said control ofllce including relay circuit means foralternately energizing and deenergizing said line wires with directcurrent to thereby cause a coded control to be transmitted to said fieldstations, said polar relay and said transformer connected to normallycause said polar relay to be actuated from its normal condition by thechange of current in said primary winding produced by operation of saidrelay circuit means from its normal condition, means governed by saidrelay circuit means for disconnecting the winding of said polar relayfrom said transformer secondary winding and for energizing said relaywith a polarity of energization to hold said relay in its normalcondition, whereby said polar relay included in said receiving apparatusis not actuated during the transmission of controls from said controlofiice.

10. A centralized traffic control system providing forv the transmissionof controls and indications between a control office and a plurality offield stations through a converter unit comprising, communicationchannels connecting said converter to said control ofiice, a line wirechan: nel connecting said converter to said field stations, saidconverter unit including transmitting means governed by said controlofiice for trans- 16 means governed by the reception at said converterunit of said indication to actuate said check relay, means governed bysaid pole-chan ing circuit means to actuate said check relay when saidindication is not being transmitted,

circuit means controlled by said check relay and mitting controls tosaid field stations, polechanging circuit means efiective duringtransmission of an indication from any of said field stations to reversethe polarity of energization on" said line wires to thereby lock out allother field stations, stick circuit means governed by said controlofiice and effective on said pole-changing circuit means to maintainsaid lock out conditions during transmission of said indication, a checkrelay operable to either of two conditions,

acting upon said stick circuit means to cause said pole-changing circuitmeans to restore the normal polarity of energization upon said linewires, whereby the transmission of indications from said field stationsis not prevented following the transmission of an indication from one ofsaid fieldstations.

11. A centralized traific control system providing for the transmissionof controls and indications between a control office and a plurality offield stations through a converter unit and comprising, a pair of linewires connecting said converter unit with said field stations,communications channels connecting said converter unit to said controloffice, said converter unit including transmitting means comprising acode responsive relay governed by said control oflice for transmittingcontrols to said field stations, a pole-changin relay efiective whenenergized during the transmission of an indication from any of saidfield stations toreverse the polarity of energization applied to saidline wires to thereby lock out all other field stations, a stick circuitfor said pole-changing relay including a normally closed contact of saidcode responsive relay; receiving apparatus at said converter unitincluding a line relay controlled by the changes in current in said linewires during the transmission of indications from said field stations, acheck relay, means including a contact of said line relay formaintaining said check relay energized during the transmission of saidindications, means including a back contact of said pole-changing relayfor normally maintaining said check relay energized when indications arenot being transmitted, circuit means governed by the deenergization ofsaid check relay for interrupting said stick circuit, whereby thefailure of said code responsive relay to pick up and effect thedeenergization of said pole-changing relay causes the picking up of saidcheck relay and the deenergization of said pole-changing relay tothereby prevent said lockout.

WILLIAM M. BARKER.

REFERENCES CITED The following references are of record in the file ofthis patent: v

' UNITED STATES PATENTS' 2,135,295 Stewartet al. o 1, 1938

